1. Field of the Invention
The present invention relates to an organo-modified silicone suitable for a mold release agent for mold casting used for mold casting of non-iron metals such as aluminum, magnesium, and zinc, and also relates to a mold release agent for mold casting comprising the organo-modified silicone, and a mold casting method using the mold release agent.
2. Related Background Art
Silicones such as dimethylsilicone, alkyl-modified silicones, alkyl- and aralkyl-co-modified silicones, and alkyl- and ester-co-modified silicones have been conventionally used as typical components in mold release agents for mold casting.
The alkyl-modified silicones, the alkyl- and aralkyl-co-modified silicones, and the alkyl- and ester-co-modified silicones have lubricity because of side chain groups thereof such as alkyl groups, aralkyl groups, and ester groups. Moreover, since the alkyl-modified silicones, the alkyl- and aralkyl-co-modified silicones, and the alkyl- and ester-co-modified silicones are gelled to form strong mold release coatings, when heated on molds. Hence, it is known that mold releasabilities of mold release agents using these silicones are further enhanced. However, although such a mold release agent can exhibit mold releasability under low-temperature conditions, the mold release agent has a problem that, when the temperature of a mold is high, sufficient mold releasability cannot be obtained because the silicone component is decomposed and volatilized. Meanwhile, although dimethylsilicone is a compound which is extremely stable even under high-temperature conditions, dimethylsilicone has a problem that the mold releasability of the obtained mold release agent is insufficient, because dimethylsilicone has high heat resistance, and hence does not form a mold release coating as described above when heated on a mold.
Meanwhile, in order to enhance the mold releasability under high-temperature conditions, developments have been made in which the adhesion of a mold release agent to a mold is improved by increasing the viscosity of an organo-modified silicone. For example, Japanese Unexamined Patent Application Publication No. Hei 09-12886 (Document 1) discloses a mold release agent using a condensation reaction product of a diorganopolysiloxane having a hydrolyzable group as a side chain, and Japanese Unexamined Patent Application Publication No. 2008-69215 (Document 2) discloses a mold release agent using a branched organo-modified silicone in which molecules of an organo-modified silicone are cross-linked with each other through a hydrocarbon group or a conjugated diene having double bonds at both terminals. However, since the diorganopolysiloxane described in Document 1 has a hydrolyzable group, the diorganopolysiloxane has a problem that, when used for a mold release agent for mold casting, the diorganopolysiloxane becomes unstable, and cannot provide a sufficient mold releasability. Meanwhile, since the branched organo-modified silicone described in Document 2 has a high viscosity, the adhesion of the obtained mold release agent to a mold is improved. However, the branched organo-modified silicone has a problem that the mold releasability of the obtained mold release agent is still insufficient, and particularly when the branched organo-modified silicone is used for an oil-based mold release agent for mold casting, the mold releasability thereof is further lowered.